1. Field of the Invention:
This invention relates to a heat exchanger using a hydrogen absorbing alloy being mainly composed of metal hydride and, more particularly, to a heat exchanger which has a hydrogen absorbing capacity, which is hard to be diminish in spite of repeated uses, which is small in size, which possess a high efficiency, and in which the adsorption and discharge of hydrogen is rapidly performed so as to be useful as an efficient hydrogen storing apparatus:
2. Prior Art:
Heretofore, there has been developed apparatus wherein hydrogen is adsorbed in a certain metal or alloy to be stored therein and transferred therefrom in the form of a metal hydride, the known apparatus has been further applied to such practical uses as the purification of hydrogen the design of heat pumps and air-conditioning systems, etc.
Since an exothermic reaction or an endothermic reaction necessarily takes place when the metal hydride adsorbs or discharges hydrogen, it is possible to make use of such a characteristic in a heat exchanger or a heat pump. In this connection, when it is intended to store or transfer the hydrogen, the delivery of hydrogen does not take place without rapid delivery of heat between the metal hydride and the outside.
However, a thermal conductivity of the hydrogen adsorption alloy itself is actually low and moreover the thermal conductivity is further lowered by the decay and micronization of the alloy along with repeated adsorptions and discharges of the hydrogen, resulting in lowering or a decline of the thermal efficiency or hydrogen adsorption capacity of the heat exchanger.
In order to overcome this problem, several attempts have been proposed to date. For example, the "Metal Hydride Reactor" disclosed in Japanese laid open patent Publication (unexamined) No. 57-61601 is characterized by holding a metal hydride in a network structure or a porous body accepted in a pressure vessel. According to one embodiment of the reactor disclosed in the 57-61601 publication, as is shown in the accompanying FIG. 12, a network (mesh-like) structure 6 comprising fine wires entwined with one another is inserted in a vessel thereby filling the vessel, and fine particles of 200 mesh pass to be held by the network structure, are infiltrated into the vessel 1a filling 50% thereof. In the vessel, heat exchange piping is arranged to serve as a heating medium reflux pipe 3, and both ends of the pipe 3 are respectively connected with an entry (supply port) 4a and an exit (exhaust port) 5a of heating medium or cooling medium. Hydrogen is introduced through inlet 2.
By the foregoing construction, it is reported that the metal hydride charged layer is improved with respect to heat conductivity by a factor of 1.9 times.
Another proposal embodiment entitled "Pressure Vessel Including a Hydrogen Adsorption member" disclosed in Japanese laid open (unexamined) Utility Model Publication No. 59-62399, and shown in the accompanying FIG. 13, is characterized by disposing hydrogen adsorbing members formed by partitioning the internal part of a vessel 1b into small spaces. To be more specific, multiple containers 7 for accepting hydrogen adsorbing members 8 are arranged in parallel in the vessel 1b. The hydrogen adsorbing members 8 are formed into a compact of square pillars, cylinders or the like and are inserted in the container 7. A drilled through hole 9 is formed through the center of each hydrogen adsorbing member 8. With such a structure, a large quantity of heat produced at the time of adsorption of the hydrogen is rapidly exchanged by the heating medium so that the reaction takes place smoothly. Fine particles in the hydrogen adsorption members 8 are prevented from being scattered or displaced when the hydrogen flows in and out.
A serious problem, however, exists in both of the foregoing two known embodiments, i.e., a rapid decline occurs in the hydrogen adsorption capacity of the hydrogen adsorption alloy itself. In other words, at an early stage of use, both of the known embodiments exhibit excellent thermal conductivity, enabling rapid adsorption and discharge of hydrogen, but with repeated and continuous use, the thermal conductivity is lowered in a rather short period of time due to the micronization etc. as a result, adsorption and discharging function decline.
Furthermore, since, when using either known embodiment, the micronization of the fine particles is unavoidable due to the decay thereof as a result of repeated expansion and contraction which takes place for every hydrogeneration and dehydrogeneration, there exists the possibility that the micronized metal hydride overcomes the constraining force of the mesh-like structure 6, drops out of the structure, and is scattered around the structure, resulting in a gradual lowering in the fine particle filling rate. Accordingly, and in the case of the second known embodiment, there exists the possibility that the compact of the hydrogen absorbing member 8 accepted in the container 7 decays and that the drilled hole is broken making it difficult to fully introduce the hydrogen gas in the longitudinal direction thereof. Moreover, the micronized fine particles are consolidated by the repeated adsorption and discharge of hydrogen, which may bring about the deformation and breakage of the container due to abnormal forces applied partially to the container. Besides, when using the second known embodiment, satisfactory workability is not secured in the process of drilling an aperture through the compact molded by compressing the fine particles of hydrogen adsorption alloy, resulting in a rough and poor finish.
In this way, in the case of the known heat exchangers, the disadvantages of decline or deterioration of heat exchanging function due to the lowering of thermal conductivity of the powdered metal hydride, decay and scattering of the fine particles along with repeated uses of the heat exchanger, still remain.